If you were not among the million or so people who immediately preordered an iPhone 4S on the day it was available, you can still upgrade your Apple handset.
If you have an older iPhone 4 or iPhone 3GS, you can upgrade it to Apple's latest mobile operating system, iOS 5, released earlier today. So, too, can iPad and iPad 2 owners, and those with a third- or fourth-generation iPod Touch. Note that many people are reporting problems with the iOS 5 installation; the following covers the basic procedure as it's supposed to go.
To get iOS 5, the first order of business is to update to iTunes 10.5. Open iTunes and then click iTunes > Check for Updates to install version 10.5.
Once iTunes is up-to-date, connect your iOS device. If you aren't prompted automatically to start downloading iOS 5, select your iPhone, iPad, or iPod Touch under the Devices header in the left-hand column and click Check for Update.
A pop-up window will appear, alerting you that a new iOS version is available for your device. Click the Download and Update button. (Or, if you are going to need your phone in the near future, opt for the Download Only button to download it now and install later. iOS 5 is a 668.8MB download for the iPhone, which could take an hour or more, depending on your connection and the amount of traffic hitting Apple's servers.)
Click through the next three screens to start the download. If you want to see its progress, click Downloads under the Store header in the left-hand column of iTunes. It shows you the estimated time remaining and how many megabytes have been downloaded.
Once the download completes, the installation will begin automatically if you chose the Download and Update option. Once iOS 5 is installed, you'll need to hop through a few setup screens on your device before it's ready to use. You'll be asked to enable location services, sign in with your Apple log-in, enter your birthday, agree to terms and conditions, set up iCloud, and enable Find My iPhone. On my iPhone 3GS, it looked like this:
To learn about all the new features iOS 5 ushers in, check out Jason Parker's full review of iOS 5.